1. Field of the Invention
The present invention relates to a focal point detection device adopting a contrast method and a camera having the focal point detection device.
2. Description of the Related Art
Camera AF (autofocus) systems in the related art include the phase difference system adopted mostly in single lens reflex cameras, the external light infrared active system generally adopted in compact cameras and the contrast system adopted in digital compact cameras. The specific AF system used in a given camera is determined primarily in correspondence to the camera type.
While an AF operation in a digital compact camera is executed by using image signals generated at an image-capturing element provided to photograph images, an image cannot always be obtained at an image-capturing element in a single lens reflex digital camera having a main mirror disposed to the front of the image-capturing surface. For this reason, an AF operation is normally executed in the single lens reflex digital camera in the phase difference method by providing an AF sensor in addition to the image-capturing element (see, for instance, Japanese Lain Open Patent Publication No. 2001-203915).
In the phase difference method, the parallax of a light flux passing through two virtual pupils set at an objective lens is detected by a light receiving element such as a CCD and the image plane distance to the focused position and the lens drive distance are calculated based upon the detection results. For this reason, the phase difference method has an advantage in that the focal point detection operation can be executed speedily. In addition, the external light method has an advantage in that the distance to the subject can be ascertained even in darkness since light is emitted from the camera. The contrast method is advantageous in that since data of a captured image are used, the focal point detection can be executed without having to provide a special mechanism and in that the focal point detection can be executed without any adjustment error by directly monitoring the state of the light receiving surface.
However, a single lens reflex camera adopting the phase difference method houses an internal AF detection device, and thus such a camera cannot be provided as a compact unit. In addition, since the state of the light receiving surface is not directly monitored, there is always the potential for an adjustment error.